How does one build a struct with an array that can be set differently for each struct, ideally by a parameter? The application being a single data type that supports arrays of different, but fixed lengths
My attempt looks somehting like this, which obviously didnt compile:
struct Data_struct(n)
{
int xData[n];
int test;
};
The only method available is to use a flexible array member.
struct Data_struct {
int test;
int xData[];
};
You would then allocate space for this using malloc():
int n = 4;
struct Data_struct *s = malloc(sizeof(struct Data_struct) + n * sizeof(int));
Note that we had to explicitly allocate additional space for the flexible array.
struct is possible.You can dynamically allocate the array
struct Data_struct
{
int * xData;
int test;
};
....
s.xData = calloc(size, sizeof(int))
and remember to free xData when finished
Data_Struct is no more a single piece of contiguous memory.Normally you would define a variable length array at the end of the struct, and then fix up the size at run-time, e.g.
typedef struct
{
int test;
int xData[1];
} Data_struct;
To allocate a struct such as this with a size of n for xData you'd do soemthing like this:
Data_struct * s = malloc(sizeof(Data_struct) + (n - 1) * sizeof(int));
One might call this ugly but here goes. Use a #define
#define foo(n) struct Data_struct##n { int test; int xData[n]; }
foo(20);
struct Data_struct20 abc;
The foo(20) defines a structure with n = 20 characters. You could use another #define for the allocation of space if you wish.
int[n] xData;wouldn't compile any ways.